1. Field cf the Invention
The present invention relates generally to an improved method for preparing vinyl chloride resin by suspension polymerization using a polymerization vessel equipped with a reflux condenser, more particularly, to a production method of vinyl chloride resin by effecting suspension polymerization while suppressing bubbling by control of an amount supplied of cooling water and hot water or steam into the reflux condenser.
2. Description of Prior Art
In the production of vinyl chloride resin a condenser has been often used in respect of safety as well as an increase in productivity. In the suspension polymerization, however, with operation of a condenser vigorous bubbling phenomenon occurs in the polymerization system and at the beginning of polymerization, in particular, foam of a suspending agent containing an initiator adheres to a gaseous portion of a polymerization vessel, inside walls of a conduit and the condenser to thus form polymer scales.
The polymer scales thus formed not only reduce the efficiency of heat transfer and invite undesired results in respect of particle size distribution, fish eyes and the like, but a great deal of labor and difficulties are necessitated for removal of the scales. Moreover, even after the middle stage of polymerization an agitating effect lowers with an increase in viscosity of a polymerized suspension liquid and hence hold-up of the suspension liquid increases concurrently with ascending of the bubbles generated.
In extreme some instances, a mixture containing monomer enters the conduit and the inside of the condenser and further polymerizes, without being mixed with the suspension liquid, to form masses of scales at that place, through which it become difficult to operate the condenser regularly and qualities of product are also deteriorated.
That is, in order to achieve stable operation of the polymerization it is necessary to prevent the suspension liquid attended by the bubbles from intruding into the condenser over an entire period of polymerization time, and to carry out the polymerization while decreasing an amount of suspension liquid to be charged into the polymerization vessel.